Thermionic tube



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THERMIONIC TUBE Filed Feb. 16, 1932 lNVENTOR Hmm; W Parker ORNY Patented Oct. 8, 1935 THERMIONIC TUBE Henry W. Parker, Toronto, Ontario, Canada, as-

signor to Rogers Radio Tubes, Limited, Toronto, Ontario,V Canada, a corporation of Ontario, Canada Application February 16, 12932, seriai No. 593,219

4 Claims. (Cl. Z50-27.5)

serves to maintain the electrodes in their proper relative positions. The entire assembly of inner screen grid, control grid, and cathode, just described, is spot-welded to supports 8 and 9 held My invention pertains to thermionic tubes and relates in particular to thermionic tubes of the so-called screen grid type.

' One of the principal objects of my invention comprises producing a screen grid tube of simpliin the press 3. 5 fied construction. y One of these supports as 8 serves as a terminal A further object comprises producing an efliand is connected by conductor 24 with the concient screen grid tube of simplified construction. tact prong 25, thus providing electrical contact A still further object comprises producing a for the inner screen grid. The outer screen 4 construction for screen grid tubes which, while consists of metal, preferably zinc, sprayed or 10 retaining the same desirable electrical character- Otherwise applied 011 the Outer Surface 0f the istics of such tubes now in use, can be fabricated envelope I and covers practically the outer surin mass production more easily and cheaply. face of the envelope exposed above the base ex- I accomplish the above desirable features and cept for a portion near the top where suflicient others which will be hereinafter pointed out and space is left to provide the necessary insulation 15 discussed by providing metallic shields 0r ferrues resistance between the control grid contact 5 and at the upper and lower extremities of the inner the metallic coating 4- This metallC @Calling screen electrode cooperating with an outer screen Serves as the outer screen usually placed within electrode which is attached to the outer surface the envelope I and adjacent to the anode 20. of the glass envelope of the tube to provide eifec- This outer screen may be, if desired, connected 20 tive screening. by means of a conductor 22 with conductor 2I,

In the drawing accompanying and forming a serving as a terminal for the cathode I2 and both part of this specication, I have illustrated a conductors Connected to Contact prong 23 in the partially sectioned elevation of my improved base of the tube, although such connection is not screen grid tube. necessary as the coating 4 may be connected to 25 Referring now particularly to the drawing, my ground in other Ways. improved tube comprises the usual glass envelope In mass production utilizing automatic exhaust I, cemented in the usual base 2. A stem 3 supmachines it is desirable to provide a slot or openports the usual anode 20 by means of standards ing 2l in the anode 20 bridged by a Wire COIlduCtOI I8 and I9, one of which, I9, serves as the ter- 26 in the form 0f a hair pin, the extremities of 30 minal therefor. The cathode I2, preferably of which are preferably spot-welded to the anode, to the indirect heated type, is provided with the allow the radio frequency currents used in heating usual heater terminals and cathode terminal as up the electrodes of the tube in the exhaust procshown in the drawing. Ihe control grid adjacent ess to quickly penetrate to the inner grids and to the cathode is formed preferably of a helix of ferrules that these elements of the tube may be 35 wire wound on supports IIl and I I and connected readily heated to redness during the exhaust procby means of conductor 6 with the control grid ess. The hair pin conductor 26 acts as a high contact 5. The inner screen grid in my improved resistance bridge across the slot in the anode and construction may be in the form of a metallic reduces the heat of the anode sufciently to allow mesh but is preferably formed of a helix of wire the grids and ferrules to quickly reach the desired 40 wound on supports I 6 and I'l and attached to temperature without unduly heating the anode.

the upper extremity of these suppo-rts by spot- Screen grid tubes now in use employ invariably welding or otherwise I provide a metallic shield an inner screen between the control grid and the or ferrule 'I. To the lower extremity of the screen anode and an outer screen adjacent the anode grid supports I6 and II, I provide a shouldered but within the glass envelope of the tube and both 45 shield or ferrule I5 which is attached to the supof these screens are electrically united with a. top ports I6 and I'I preferably by spot-welding. The screen or cover entirely covering the upper part shoulder of shieldV or ferrule I5 supports a disk of the ano-de, in order that the control grid lead or washer I4 of mica or other refractory insulator terminal may be shielded. 50

I have found by experiment that my simplified construction produces exactly the same degree of shielding as the usual type just referred to and yet that a tube constructed in accordance with my invention evidences the same desirable low capacitance between the control grid and the anode 55 ing material which serves to support the standards IG and I I which, in turn, support the control grid helix. The upper extremity of both the cathode I2 and control grid supports pass through openings provided in a disk or washer I3 of mica or other refractory insulating material which struction in mass production is greatly simplied and consequently cheapened. It will be further observed that all of the electrodes in the sub-assembly can be definitely iixed with respect to their relation and that the sub-assembly can be fabricated in quantity and held in stock without deterioration or change in relative position of the electrodes until desired for complete assembly of the tube, a feature obviously advantageous in mass production. v

I have found by experiment that the metal shields or ierrules 1 and I5 when provided in the relative positions shown in the drawing cooperate with the exterior screen 4 to function in exactly the same manner as the screens now used in such tubes and that therefore my simplified construction while producing a tube which may be more easily and cheaply constructed in mass production performs exactly similar to similar tubes now in use.

Having thus completely described my invention, what I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A thermionic tube comprising, an enclosing envelope, a press within said envelope, a screen grid comprising a pair of metallic ferrules and a metallic mesh therebetween supported by said press, a control grid supported by said screen grid, a cathode within said control grid, an anode supported by said press and partially surrounding said screen grid, the opening in said anode being bridged by a conductor, the electrical resistance of. which is much higher than the electrical resistance of said anode. 5

2. A thermionic tube comprising, an enclosing envelope, a press within said envelope, a screen grid comprising a pair of metallic ferrules and a metallic mesh therebetween supported by said press, a control grid within said screen grid, a 10 cathode within said control grid and an anode, a portion of which consists of a conductor having a higher electrical resistance than the remaining portion surrounding said screen grid and supported by said press. l5

3. A thermionic tube comprising, an enclosing envelope, a press within said envelope, a pair of standards supported by said press, said standards supporting a screen grid in the form of a pair of standards having a Wire helix on the midportion and a metallic ferrule on each extremity thereof, a control grid Within said screen grid and supported thereby, a cathode within said control grid and an anode Without said screen grid and supported by said press, said anode being provided with a slot bridged by a conductor in the form of a looped wire.

4. A thermionic tube comprising, an enclosing envelope, a press within said envelope, a pair of standards supported by said press, said standards Y supporting a screen grid in the form of a pair of standards having a Wire helix on the mid-portion and a metallic ferrule on each extremity thereof,

a control grid within said screen grid, a cathode within said control grid and an anode without said screen grid and supported by said press, said anode being provided with a slot bridged by a conductor in the form of a looped Wire.

HENRY. W. PARKER. 

